Recycling generated carbon dioxide back to fuels and chemicals would make a tremendous difference to the U.S. economy. Presently, fuels and organic chemicals are usually made from petroleum, coal, and/or natural gas “fossil fuels.” However, if such fuels and chemicals could be made from CO2, then the U.S. dependence on imported oil would be lessened, and emissions of greenhouse gases that are thought to contribute to global warming would be reduced. CO2 produced in power plants would change from a waste product to a useful, economically viable feedstock. Solar and wind energy could also be stored in the form of hydrocarbon fuels.
Presently, however, most large volume organic chemicals are made from fossil fuels. For example, most acrylic acid produced in the U.S. is currently made from propylene. The propylene is made from petroleum. Most formaldehyde now produced in the U.S. is manufactured by oxidation of methanol. The methanol is manufactured from natural gas or coal. Ethylene is made by cracking of light olefins from petroleum, or from methanol. If these products could be made from CO2, the use of fossil fuels in the U.S. would be reduced, as would the emissions of greenhouse gases.
U.S. Pat. No. 8,212,088 describes an environmentally beneficial process for preparing a fuel or chemical, in which carbon dioxide from a natural source, or carbon dioxide from an artificial chemical source that would otherwise be discharged into the environment by the artificial chemical source, is converted to useful fuels and chemicals. In the process described in the '088 patent, CO2 is first converted to a mixture of formic acid and other compounds. The formic acid is then sent to a second process where it undergoes a 4-electron hydrogenation to form methanol. The methanol is then converted to fuels and chemicals using conventional chemical processes, as illustrated in FIG. 1. The advantage of converting CO2 to methanol is that infrastructure already exists to convert methanol into other products.
The limitation in the process described in the '088 patent is that the hydrogenation to methanol is an extra step in the conversion process that wastes energy, and that may not be needed at all. For example, almost half of the methanol produced worldwide is further reacted to yield formaldehyde via an oxidative dehydrogenation process. Energy is wasted when formic acid is first hydrogenated to methanol and then dehydrogenated to formaldehyde, as illustrated in FIG. 2A. Moreover, the intermediate methanol can be a safety hazard, because it is highly flammable and the flame is invisible.
As described in more detail below, the present environmentally beneficial process for the production of fuels and chemicals preferably employs carbon dioxide from a natural source or carbon dioxide from an artificial chemical source that would otherwise be discharged into the environment by the artificial chemical source. The carbon dioxide is converted to formic acid and other products. The formic acid is then converted to fuels and/or chemicals without the intermediate process of hydrogenating the formic acid to methanol or reacting the formic acid with ammonia to form formamide.
By contrast, the '088 patent describes a method in which (a) carbon dioxide is converted to formic acid and other products, (b) the formic acid is hydrogenated to form methanol, and then (c) the methanol is converted to fuels and chemicals. For example, FIGS. 2A and 2B compare the process for the formation of formaldehyde disclosed in the '088 patent (FIG. 2A) and that disclosed in the present application (FIG. 2B). As shown, the process disclosed in the present application uses half as much hydrogen as the process described in the '088 patent, and does not require temperatures as high as those used in the process described in the '088 patent.
In the process disclosed herein, only a small fraction (namely, less than 10%) of the formic acid is hydrogenated to methanol. In the present process, formic acid can be made by any method, and the formic acid is then converted to fuels and chemicals without the intermediate process of hydrogenating the formic acid to methanol or reacting it with ammonia to form formamide. The present process produces fuels and chemicals in which formic acid is converted to one of seven primary feedstocks: formaldehyde, acrylic acid, methane, ethylene, propylene, syngas, and C5-C7 carbohydrates, without the intermediate process of hydrogenating the formic acid to methanol or reacting it with ammonia to form formamide. The formaldehyde, acrylic acid, methane, ethylene, propylene, syngas and/or short chain carbohydrates can either be used directly, or can be converted into a wealth of other products, as illustrated in FIG. 3. The list of products in FIG. 3 is not meant to limit the present process. Rather, it provides examples of products that can be made from formic acid following the teachings of this application.
In the present process for the production of formaldehyde, and products made using formaldehyde, formic acid is converted to formaldehyde without a separate intermediate process of hydrogenating the formic acid to methanol. The present process encompasses processes in which hydrogen reacts with formic acid to form formaldehyde. The process can occur in the presence of a catalyst comprising an oxide of at least one of the following elements: Mg, Ca, Sr, Ba, Ti, Y, Lu, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Tl, Si, Ge, Sn, Sb, Bi, Se, Te, Pb, La, Ce, Pr, Th, Nd, Pm, U, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb, preferably the oxides of cerium or tellurium. Reaction temperature can be between 8° C. and 350° C., preferably between 40° C. and 200° C., most preferably between 60° C. and 100° C.
The present process also produces organic acids with at least three carbon atoms specifically including acrylic acid, methyl acrylic acid or propionic acid, wherein formic acid directly or indirectly reacts with an unsaturated hydrocarbon to yield the organic acid. The present process encompasses systems for produce the organic acids from formic acid and an unsaturated hydrocarbon comprising at least two reactors in series, in which the temperature of each reactor can be controlled independently. The present process also encompasses systems with one reactor containing an acid catalyst and a second reactor containing a catalyst comprising at least one of a nickel salt, a copper salt and a palladium salt.
The present process also produces olefins such as ethylene and propylene and products synthesized from olefins, in which formic acid is converted to the olefins ethylene and/or propylene without a separate intermediate process of hydrogenating the formic acid to methanol. In the present process, formic acid is first converted to formaldehyde as described above and the formaldehyde is then further converted to olefins such as ethylene, propylene or butylene. The process can employ a base catalyst to condense the formaldehyde into a multi-carbon species, followed by an acid catalyst to convert the multi-carbon species into olefins. The acid catalyst can be in the form of a zeolite such as ZMS-5 or SAPO-43. The present process encompasses the use of CO2 to modify the pH of the mixture after some of the formaldehyde has been condensed. In some embodiments, the present process employs ZSM-5 or SAPO-43 in the conversion of formic acid to a product comprising propylene. ZSM-5 is an aluminosilicate zeolite mineral belonging to the pentasil family of zeolites, having the chemical formula is NanAlnSi96-nO192.16H2O (0<n<27); it is widely used in the petroleum industry as a heterogeneous catalyst for hydrocarbon isomerization reactions (see http://en.wikipedia.org/wiki/ZSM-5, downloaded on Feb. 23, 2013). SAPO-43 is a small pore silico-alumino-phosphate (see http://pubs.acs.org/doi/abs/10.1021/1a026424j, downloaded on Feb. 23, 2013).
The present process also produces carbohydrates or molecules produced from carbohydrates, in which formic acid is converted to a carbohydrate without a separate intermediate process of hydrogenating the formic acid to methanol. In the present process, the formic acid is converted to formaldehyde as described above, and the formaldehyde is then reacted in the presence of a base catalyst to yield a carbohydrate. Calcium hydroxide is a preferred catalyst in the present process, and the present process specifically encompasses the use of carbon dioxide for the removal of calcium from solution.
The present process also produces syngas or molecules produced from syngas, in which formic acid is converted to syngas without a separate intermediate process of hydrogenating the formic acid to methanol. The present process preferably employs two parallel reactors to convert the formic acid into syngas, wherein the temperatures of the two independent reactors can be independently controlled. It is preferred that one of the reactors contains an acid catalyst while the other reactor preferably contains a metallic catalyst.